The Afghan police force has been a target of Taliban whose members often infiltrate it to carry out attacks. Photograph: Johannes Eisele/AFP/Getty Images

An Afghan policeman shot dead nine of his fellow officers as they slept in a village in aTaliban stronghold on Friday, police said.

The gunman opened fire with his assault rifle after waking up at 3am apparently to take over guard duty at a small command post in Paktika province, killing everyone inside, including the commander. He then took their weapons, piled them in a pickup truck and sped away.

The incident is latest among a number of attacks by Afghan security forces against their own people or against international troops in Afghanistan in recent years, some the result of arguments and others by infiltrators.

Provincial police chief Dawlat Khan Zadran said the incident took place in Yayakhil town of Yayakhil district.

Khan said his own brother was among those killed, along with the commander of the post, identified as Mohammad Ramazan, and two of the commander's sons.

The motive for the killing was not known, but police in the area blamed the Taliban for the attack. Paktika is a stronghold of the Haqqani network, a Pakistan-based group with ties to the Taliban and al-Qaida. Although they mostly attack US-led coalition forces, they have often carried out assaults and bombings against the Afghan army and police.

Taliban spokesman Zabiullah Mujahid claimed responsibility for the attack and said the shooter was a member of an insurgent group. He said the dead police officers weapons were handed over to the Taliban.

Khan and Zadran said the killer's two brothers were being held for questioning.

The increasing number of attacks by Afghan police and soldiers has cast doubt on the readiness of Afghan forces to take over their own security as the US prepares to end its combat mission by the end of 2014.

So far this year, 16 Nato soldiers have been killed by Afghan soldiers and policemen or militants disguised in their uniforms. That equals 18% percent of the foreign troops killed this year in Afghanistan.

There has also been an increase in Afghans killing their own comrades. A member of a village-level force that provides security in areas where the Afghan army and police cannot was accused of involvement in the killing of nine members of his unit in March in southern Uruzgan province. They also were shot dead while asleep at their post in the village of Oshi in the province's Charchino district.

The village units known as Afghan Village Police or ALP, are trained by the US but run by the Afghan government and police.

Taliban infiltration of the ALP is considered more difficult as all their members are recruited locally and vetted by village elders before joining.

In other violent incident on Friday, a motorcycle bomb exploded, killing an Afghan police officer and wounding another in Sangin district of Helmand province. Police said another officer was also killed late on Thursday outside his house in Lashkar Gah, the capital of Helmand.

Nato said two of its service members were killed in southern Afghanistan – one died in a roadside bomb explosion on Friday and the other in an insurgent attack on Thursday.

So far this year, 88 international troops have been killed in Afghanistan.